Post on 02-Jan-2016
Lecture Cell
Chapters 5 and 6 Biological Membranes and
Cell Communication
Membrane structure, I
Selective permeability Amphipathic~
hydrophobic & hydrophilic regions
Singer-Nicolson: fluid mosaic model
Fig. 5-6, p. 111
Glycoprotein
Glycolipid
Cytosol
Hydrophilic
Carbohydratechain
Hydrophilic
HydrophobicExtracellular fluid
Cholesterol
α-helix Integralproteins
Peripheralprotein
Carbohydratechains
Membrane structure, II
Phospholipids~ membrane fluidity Cholesterol~ membrane stabilization “Mosaic” Structure~ Integral proteins~ transmembrane
proteins Peripheral proteins~ surface of
membrane Membrane carbohydrates ~ cell to
cell recognition; oligosaccharides (cell markers); glycolipids; glycoproteins
Fig. 5-2b, p. 108
Integral(transmembrane)
protein
(b) Fluid mosaic model. According to this model, a cellmembrane is a fluid lipid bilayer with a constantly changing“mosaic pattern“ of associated proteins.
Phospholipidbilayer
Peripheralprotein
Hydrophilicregion of protein
Hydrophobicregion of protein
The Lipid Bilayer
Lipids of the bilayer fluid or liquid-crystalline state
Proteins move within the membrane
Membrane Proteins
Functions of Membrane Proteins
Membrane traffic Diffusion~ tendency of any
molecule to spread out into available space
Concentration gradient Passive transport~ diffusion
of a substance across a biological membrane without using energy
Osmosis~ the diffusion of water across a selectively permeable membrane
Diffusion
Osmosis
Fig. 5-12, p. 117
Pressure appliedto piston to resistupward movement
Watermolecule
Selectivelypermeablemembrane
Pure water
Moleculeof solute
Waterplussolute
Water balance Osmoregulation~ control
of water balance
Hypertonic~ higher concentration of solutes
Hypotonic~ lower concentration of solutes
Isotonic~ equal concentrations of solutes
Cells with Walls: Turgid (very firm)
Flaccid (limp)
Plasmolysis~ plasma membrane pulls away from cell wall
Osmotic Pressure
Fig. 5-13a, p. 118
SolutemoleculesNo net water
movement
(a) Isotonic solution.When a cell is placed in anisotonic solution, watermolecules pass in and outof the cell, but the netmovement of watermolecules is zero.
Outsidecell
Insidecell
H20molecules
Fig. 5-13b, p. 118
Outsidecell
(b) Hypertonic solution.When a cell is placed in ahypertonic solution, thereis a net movement ofwater molecules out of thecell (blue arrow). The cellbecomes dehydrated andshrunken.
Net water movementout of the cell
Insidecell
Fig. 5-13c, p. 118
10 μ
m
(c) Hypotonic solution.When a cell is placed in ahypotonic solution, the netmovement of watermolecules into the cell(blue arrow) causes the cellto swell or even burst.
Insidecell
Outsidecell
Net water movementinto the cell
Turgor and Plasmolysis
Fig. 5-14, p. 119
Plasmamembrane
Vacuole
Vacuolarmembrane(tonoplast)
Vacuole
Cytoplasm
Plasmamembrane Nucleus
Specialized Transport
Transport proteins Facilitated diffusion~
passage of molecules and ions with transport proteins across a membrane down the concentration gradient
Active transport~ movement of a substance against its concentration gradient with the help of cellular energy
Facilitated Diffusion
Fig. 5-16a, p. 120
1 Glucose binds to GLUT 1.
Cytosol
Lowconcentrationof glucose
Glucosetransporter(GLUT 1)
Highconcentrationof glucose
Glucose
Outside cell
Fig. 5-16b, p. 120
GLUT 1 changes shape andglucose is released inside cell.
2
Fig. 5-16c, p. 120
GLUT 1 returns to its originalshape.
3
Types of Active Transport Sodium-potassium pump Exocytosis~ secretion of
macromolecules by the fusion of vesicles with the plasma membrane
Endocytosis~ import of macromolecules by forming new
vesicles with the plasma membrane
•phagocytosis•pinocytosis•receptor-mediated endocytosis (ligands)
Fig. 5-17a, p. 121
(a) The sodium–potassium pump is a carrier protein that requiresenergy from ATP. In each complete pumping cycle, the energy ofone molecule of ATP is used to export three sodium ions (Na+)and import two potassium ions (K+).
So
diu
mco
nce
ntr
atio
n g
rad
ien
t
Lower
Higher
Cytosol
Outsidecell
Activetransportchannel
Lower
Higher
Po
tass
ium
c on
c en
trat
ion
gr a
die
nt
Fig. 5-17b, p. 121
1. Three Na+ bindto transport protein.
2. Phosphate group istransferred from ATPto transport protein.
3. Phosphorylationcauses carrier proteinto change shape, releasing3 Na+ outside cell.
4. Two K+ bind totransport protein.
5. Phosphate is released.6. Phosphate release causescarrier protein to returnto its original shape. TwoK+ ions are released insidecell.
Phagocytosis
Large particles enter cell
Receptor-MediatedEndocytosis
Intracellular junctions PLANTS: Plasmodesmata: cell wall
perforations; water and solute passage in plants
ANIMALS: Tight junctions~ fusion of
neighboring cells; prevents leakage between cells
Desmosomes~ riveted, anchoring junction; strong sheets of cells
Gap junctions~ cytoplasmic channels; allows passage of materials or current between cells
Tight Junctions
Gap Junctions
Cell Signaling
1. Synthesis, release, transport of signaling molecules
- neurotransmitters, hormones, etc- ligand binds to a specific receptor
2. Reception of information by target cells
Cell Signaling
3. Signal transduction- receptor converts extracellular signal into
intracellular signal- causes change in the cell
4. Response by the cell
Cell Signaling
Fig. 6-2, p. 136
Signalingprotein
Protein thatregulates a gene
Alteredgene activity
EnzymeProtein
Alteredmembrane
permeability
Alteredmetabolism
Response
Signaltransduction
Cell sendssignal
Reception
Receptor
Signalingmolecules
1
2
3
4
Local Regulators
Paracrine regulation diffuse through interstitial fluid act on nearby cells
Local regulators histamine growth factors prostaglandins nitric oxide
Local Signals
Neurotransmitters
Chemical signals released by neurons (nerve cells)
Hormones
Chemical messengers in plants and animals
Secreted by endocrine glands in animals
Transported by blood to target cells
Hormones